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Effect of grazing management on herbage protein concentration, milk production and nitrogen excretion of dairy cows in mid‐lactation
Author(s) -
Bryant R. H.,
Dalley D. E.,
Gibbs J.,
Edwards G. R.
Publication year - 2014
Publication title -
grass and forage science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.716
H-Index - 56
eISSN - 1365-2494
pISSN - 0142-5242
DOI - 10.1111/gfs.12088
Subject(s) - pasture , grazing , lactation , zoology , excretion , morning , chemistry , perennial plant , milk production , dairy cattle , rumen , agronomy , biology , food science , botany , fermentation , pregnancy , genetics , biochemistry
Abstract The objective of this experiment was to use diurnal and temporal changes in herbage composition to create two pasture diets with contrasting ratios of water‐soluble carbohydrate ( WSC ) and crude protein ( CP ) and compare milk production and nitrogen‐use efficiency ( NUE ) of dairy cows. A grazing experiment using thirty‐six mid‐lactation F riesian x J ersey cows was conducted in late spring in C anterbury, N ew Z ealand. Cows were offered mixed perennial ryegrass and white clover pastures either in the morning after a short 19‐day regrowth interval ( SR AM ) or in the afternoon after a long 35‐day regrowth interval ( LR PM ). Pasture treatments resulted in lower pasture mass and greater herbage CP concentration (187 vs. 171 g kg −1 DM ) in the SR AM compared with the LR PM but did not affect WSC (169 g kg −1 DM ) or the ratio of WSC / CP (1·0 g g −1 ). Cows had similar apparent DM (17·5 kg DM cow −1 d −1 ) and N (501 g N cow −1 d −1 ) intake for both treatments. Compared with SR AM cows, LR PM cows had lower milk (18·5 vs. 21·2 kg cow −1 d −1 ), milk protein (0·69 vs. 0·81 kg cow −1 d −1 ) and milk solids (1·72 and 1·89 kg cow −1 d −1 ) yield. Urinary N concentration was increased in SR AM , but estimated N excretion and NUE for milk were similar for both treatments. Further studies are required to determine the effect of feeding times on diurnal variation in urine volume and N concentration under grazing to predict urination events with highest leaching risk.